As information technology like ATM and Ethernet or the like develops recently, communication cable appears to be more important.
Generally, UTP (Unshielded Twisted Pair) cable which is used for communication cable is fabricated in the following steps: electric wires consist of conductor such as copper or etc. coated by insulation coating are twisted to form twisted pairs, then four twisted pairs are collected and coated by insulation coating.
It has been desired to increase the information transmitting capacity of the communication cable, and the communication cable has been developed to increase its information transmitting capacity.
In the meanwhile, the communication cable are classified by the identification characters such as category (or Cat.) and number in accordance with its signal transmitting capacity under international agreement, wherein the bigger number means the higher transmitting capacity.
For example, communication of Cat.3 can transmit signal of 16 MHz, Cat.4 can 20 MHz, and Cat.5 can 100 MHz, wherein the higher modulation frequency is used, the more informations can be transmitted.
However, as the higher modulation frequency is used, the noise due to the cross talk among the cables and change of the impedance in the conducting wires is increased, which results in a problem that the assortment of the signals gets more difficult in the signal receiver.
For this reason, up to recently, the limit of the UTP cable's signal transmitting capacity has been seemed to be around 155 Mbps (Megabit per sec).
However, as the technology of information transmitting equipment develops recently, the signal worsening due to the cross talk in the cable can be compensated by way of compensation method using DSP (digital signal processing) equipment and etc, so it is possible to transmit 1,000 Mbps (1 Gbps) using Cat.5e, and the standard committee of IEEE (Institute of Electrical and Electronics Engineers) officially decided 1000 Base-T as the standard of Ethernet in the year of 1999.
In the meanwhile, in view of the developing trend of the related technology such as movie transmission technology and etc, the cable which can transmit information in a higher level will be needed in the near future, so that major cable manufacturers and related system manufacturers are competitively investing for satisfying this need, and also in the IEEE a specialized committee is organized for standardization on high speed information transmission cable.
However, for improvement of the transmission capacity, usually higher frequency is used, and that results in problems of proportional increase of insertion loss, impedance mismatching between electric wire and equipment, cross talk between wires.
Representative cross talk are RL (Return Loss), NEXT (Near End Cross Talk), FEXT (Far End Cross Talk) and etc, to solve these, compensation in transmission system and change of pitch, diameter of conductor, diameter of wire, shape of cross filler has been tried.
Overviewing patents related to improvement of UTP cable's transmission capacity, cross talk between wires has been seemed to be important factor for worsening of transmission quality, a lot of effort has been done to solve said problem.
Related important patents are U.S. Pat. No. 5,132,488, U.S. Pat. No. 5,969,295, U.S. Pat. No. 5,519,173, U.S. Pat. No. 5,952,615 etc, to overviewing the contents, to improve transmission capacity those present positioning metal foil in sheath, constraining cross talk by inserting filler.
Moreover, recently useful band of frequency is expanded to at least 400 MHz, particularly 500-650 MHz, band of high frequency is used for high transmission capacity more than 20 Gbps in theoretical transmission capacity (Shannon Capacity), in practical transmission capacity 10 Gbps.
In case of using band of high frequency, it is important problem to minimize noise in cable by matching impedance of wire in cable to international standard of 100 ohm around so matching impedance between cable and equipment.